Digital content including music, video, and game programs is typically recorded on a recording medium such as a CD or a DVD for distribution purposes. For digital content, various approaches to copyright protection have been attempted. As an example of such approaches, a technique is known with which encrypted content, i.e., an encryption result of digital content, is recorded on a recording medium and which only the content player that is allowed to play the digital content is permitted to decrypt and play the encrypted content. Such a technique is disclosed in, for example, Dalit Naor, Moni Naor, and Jeff Lotspiech, “Revocation and Tracing Scheme for Stateless Receivers” (CRYPTO '01, Lecture Notes in Computer Science 2139, pp. 41-62, Springer-Verlag, 2001) (“Document 1”).
On the recording medium, recorded in addition to encrypted content are information (hereinafter, referred to as “decryption information”) for the decryption of the encrypted content, and information (hereinafter, referred to as “management information”) such as TOC (Table Of Contents) that is used for managing the recording medium. The management information is typically recorded in an area that is different from the area where the encrypted content is recorded. For example, in the recording media such as DVDs, the management information is recorded in a more secure area, such as a lead-in (Lead-in) area, having a much smaller physical storage capacity as compared with an area where encrypted content is recorded.
The decryption information includes at least one of information about a player that is allowed to decrypt and play the encrypted content and information about an unauthorized player that is not allowed to do so. This prevents an unauthorized player from playing content. When an unauthorized player is newly added, the decryption information is updated to cope with the revocation of the unauthorized player. Though depending on the approach for the revocation, the data size of the decryption information that should be recorded on the recording medium becomes larger as the number of the players to be revoked is increased when a typical method such as the CS (Complete Subset) scheme and the SD (Subset Difference) scheme described in Document 1 is used.
As described above, the area in which the management information is to be recorded is physically small in storage capacity. Therefore, when having a large data size, the management information may not fall within a highly secure area that is originally intended for recording it. In particular, the data size of the decryption information may be increased, causing a problem of not being able to record, after the upgrading, the decryption information which can originally be recorded in an area of a higher security level on the recording medium. This limits, for example, the number of the players that should be revoked for their decryption and their play, and the number of the players that should be revoked cannot thus be increased more than a certain number.
The present invention is directed to provide a recording medium on which whole pieces of information such as the management information that is intended to be recorded in an area of a higher security level is recorded while keeping the management information secure, even when it is larger in data size than the storage capacity of the area originally intended for recording it, and a technique to play the recording medium.